The present invention relates to an ultrasonic probe device having an ultrasonic probe for transmitting ultrasonic waves toward and receiving ultrasonic echoes from a target region in a body under examination, and an ultrasonic coupler for being interposed between the ultrasonic probe and the surface of the body.
One conventional ultrasonic probe device comprising an ultrasonic probe and an ultrasonic coupler is illustrated in FIGS. 12 and 13 of the accompanying drawings.
The ultrasonic probe device, generally denoted at 20 in FIG. 12, includes an ultrasonic probe 21 for transmitting ultrasonic waves and receiving ultrasonic echoes, and an ultrasonic coupler 22 having a mount 23 by which the ultrasonic coupler 22 is mounted on the ultrasonic probe 21 and a surface 24 for contacting the surface 25 (FIG. 13) of a body M being examined, the ultrasonic coupler 22 containing an acoustic medium such as water. The ultrasonic coupler 22 is in the form of a water bag or a soft container housing a soft colloidal material or the like. Therefore, the ultrasonic coupler 22 is flexible enough to allow the contacting surface 24 to be of a flat, symmetrical shape with respect to a central line BMc in the plane in which an ultrasonic beam BM is scanned, or to be freely deformed.
The ultrasonic probe 20 may be used to obtain Doppler information (FFT Doppler information, two-dimensional color Doppler information) on a peripheral blood vessel 26 such as a carotid artery running substantially parallel to the surface 25 of the body M. However, most important Doppler information on a central area of the ultrasonic beam BM, i.e., a central area of a target region 27, may not be accurately obtained or may not entirely be measured. This results from the principles of the Doppler effect. More specifically, the relationship between a Doppler shift frequency fd and a blood speed V is expressed by: ##EQU1## where .alpha. is the angle formed between the ultrasonic beam and the blood stream, f is the driving frequency, and C is the speed of sound in the body being examined. Since the angle .alpha. between the blood stream and the ultrasonic beam BM is 90.degree. in the target region 27, fd=0 and the speed of the blood flow cannot be measured.
Another cause of the trouble is that the flat symmetrical contacting surface 24 of the ultrasonic coupler 22 causes multiple reflections of the ultrasonic echo.
As described above, the conventional ultrasonic probe device cannot obtain accurate Doppler information on the central area of the target region to be measured.